A. Field of the Invention
This invention relates to apparatus for positioning a mobile rig adjacent to a structure, and more particularly to apparatus for elevating the rig to an elevation above ground level.
B. Background of the Prior Art
At times during the life of an oil and gas well, it is necessary to perform workover operations. Workover operations are frequently performed by positioning over the wellhead a structure on which workmen may work and positioning adjacent to the structure a rig having a mast for running equipment in and out of the well.
In certain locations, wellheads are exceedingly tall, and available structures do not have sufficient clearance thereunder to clear the wellhead. It is possible to provide higher structures, but commercially available self-propelled carrier rigs do not have masts tall enough to allow operation between the surface of the platform and the top of the mast. One solution would be to procure a rig with a longer mast, but such rigs are not available. Another solution would be to elevate the rig, as for example by placing a platform adjacent to the structure with a ramp extending laterally away therefrom.
Self-propelled rigs must be substantially level when they are in operation. This would require a level platform of substantially the same length as the rig. Since mobile rigs are limited in the incline up which they can travel, a relatively long ramp would be required. The combination of a platform and a ramp would have a length approximately twice that of the rig and in order to line up the rig for travel up the ramp, a space of at least three, and more probably four, rig lengths away from the wellhead is necessary. In a number of instances, such space simply is not available. Additionally, in order to transport a ramp and platform, extra equipment-carrying capacity is required.